Field of the Invention
The present invention relates to power supply control of an information processing apparatus such as an image forming apparatus.
Description of the Related Art
In recent years, there have been printers having a power supply ON/OFF switch (a secondary switch) only for a secondary-side power supply, for control of a printer power supply and cost reduction. This type of printers do not have a primary-side power supply switch, which is provided to interrupt a primary-side voltage (an alternating current (AC) voltage) supplied to the printer.
In such printers, a central processing unit (CPU) monitors ON/OFF of the secondary switch. Therefore, when the CPU is out of control or freezes, the power supply cannot be turned off even if the power supply switch is turned off. To address this situation, some of the printers have a power supply OFF timer used to forcibly turn off the power supply, when the CPU is in a state such as being out of control. In this type of printers, the power supply OFF timer is set so that the power supply is automatically turned off after a lapse of a predetermined period of time, when the power supply switch on the secondary side is turned off.
For example, Japanese Patent Application Laid-Open No. 10-78832 discusses a shutdown device. When a power supply switch is turned off, this shutdown device causes a workstation to start a shutdown sequence, so as to forcibly interrupt supply of power to the workstation after a fixed period of time.
Usually, when a shutdown sequence is performed on a controller side, it is necessary to shut down a lot of complicated systems such as a memory, in specific order. Therefore, time necessary for the shutdown sequence is estimated, and this necessary time is set in a power supply OFF timer. However, with complication of the systems, the time necessary for the shutdown sequence has increased and therefore, the time set in the power supply OFF timer has increased as well. For this reason, it takes a long time to complete interruption of a voltage supplied to a high voltage unit such as a printer. Thus, in a conventional image forming apparatus, when a CPU is out of control, it takes a long time before supply of power to a high voltage unit is interrupted, after a power supply switch is turned off by a user.